The present invention relates to a turn-limited column assembly for use in an automotive steering system or the like, and, in particular, to a turn-limited column assembly that utilizes a sliding element disposed in spiral tracks to limit rotation of the column
A typical automotive vehicle includes a steering wheel that is rotated by an operator to turn the vehicle wheels and thereby change direction of the vehicle. The steering wheel is mounted on a column that is mechanically coupled to the wheels. The direction of the wheels during turning is limited by mechanical stops. Thus, when the wheels reach a predetermined direction corresponding to a minimum turning radius of the vehicle, the wheels engage the stops. The mechanical coupling prevents the operator from further turning the steering wheel. In this manner, the operator is made aware that the minimum turn radius has been attained.
It has been proposed to utilize a steer-by-wire system that eliminates the mechanical connection between the operator and the vehicle wheels. In order to replicate the driving experience of a typical operator, a steer-by-wire system uses a steering wheel and steering column similar to those found in a mechanically-coupled vehicle. A sensor is operatively coupled to the column and generates an electrical signal in response to rotation of the column. This electrical signal is then transmitted to an electronic actuator, such as a motor, which turns the wheels in a desired direction. Because there is no mechanical coupling, even when the steerable wheels are prohibited from turning, the steering wheel may be rotated. Continued rotation of the steering wheel may cause damage to the sensor. Moreover, the operator is not aware that further rotation of the steering wheel is not effective in turning the vehicle.
One feature of a typical mechanically-coupled system is that the steering wheel rotates more than 360 degrees in each direction when turning the vehicle. In order to replicate the sensitivity of a mechanically-coupled system, it is desired that the operator also be able to rotate the steering wheel in a steer-by-wire vehicle more than 360 degrees. Thus, there is a need for a steering column assembly that is adapted for use in a steer-by-wire system and replicates familiar experience of a mechanically-coupled steering system by permitting the operator to freely rotate the steering wheel more than 360 degrees in each direction, but includes a turn-limiting mechanism that is effective to prevent the steering-wheel from being rotated beyond a point where further rotation is no longer effective in turning the wheels and that may be readily manufactured and incorporated into the steering column assembly without interfering with the steer-by-wire sensor or other components thereof.
The present invention is a turn-limited column assembly comprising a column rotatable about an axis and a first plate rotatable with the column. The first plate defines a first spiral track having an inboard end and an outboard end. The invention further comprises a second plate disposed to permit rotation of the first plate relative to the second plate. The second plate defines a second spiral track having an inboard end and an outboard end. The plates are arranged such that a section of the first track axially overlies a section of the second spiral track to define an intersection. The first spiral track extends from the intersection toward the inboard end of the first spiral track in a first direction, and the second spiral track extends from the intersection toward the inboard end of the second spiral track in a second direction different from the first direction. A sliding element is disposed at the intersection and is slideable along the first track and the second track. The sliding element, the first spiral track and the second spiral track cooperate to permit rotation between a first stop where the sliding element is disposed at the inboard end of the first track and the inboard end of the second track and a second stop where the sliding element is disposed at the outboard end of the first track and the outboard end of the second track.